Calculate Sourdough Hydration (Formula + Step-by-Step)

Calculating sourdough hydration by hand teaches you how bakers think. Once you understand the math, you can troubleshoot recipes and adjust on the fly. This step-by-step guide walks you through the process—and when you're done, our sourdough hydration calculator will save you time on every bake.

Step 1: Understand the Basic Formula

The sourdough hydration formula is simple:

Hydration % = (Total water ÷ Total flour) × 100

That's it. But "total" means everything—main dough plus starter. This is where beginners get tripped up.

Step 2: Identify Your Starter's Hydration

Most starters are 100% hydration: equal flour and water by weight. So 100g of 100% hydration starter = 50g flour + 50g water. If you use a stiffer starter (e.g., 50% hydration), the math changes. For this guide, we'll assume 100%.

Step 3: Calculate Flour and Water in Your Starter

If you're using 150g of 100% hydration starter:

• Starter flour = 150 ÷ 2 = 75g
• Starter water = 150 ÷ 2 = 75g

For 80% hydration starter (stiffer): flour = 150 ÷ 1.8 ≈ 83g, water ≈ 67g. Use the formula: flour = starter weight ÷ (1 + hydration as decimal).

Step 4: Add Main Dough Ingredients

Suppose your main dough has 400g flour and 280g water. Add the starter amounts:

• Total flour = 400 + 75 = 475g
• Total water = 280 + 75 = 355g

Step 5: Apply the Formula

Hydration = (355 ÷ 475) × 100 = 74.7%

Your dough is approximately 75% hydration. This matches a medium-hydration artisan loaf.

Step 6: Work Backwards (Recipe Design)

Often you want a target hydration and dough weight. Say you want 800g dough at 72% hydration. The formula gets more complex because flour and water also need to account for salt and levain. This is why bakers use baker's percentage—and why our sourdough hydration calculator exists. See our baker's percentage guide for the full system.

Common Calculation Mistakes

Mistake 1: Forgetting the starter. Your levain adds significant flour and water. Always include it. Mistake 2: Using volume. Cups of flour can vary by 30% depending on how you scoop. Weight only. Mistake 3: Ignoring flour type. Whole wheat absorbs more—our calculator's flour mix options adjust for this. Mistake 4: Including salt. Salt doesn't go in the hydration formula; it's calculated separately as a percentage of flour.

When to Use a Calculator

Manual calculation is great for learning. But for every bake? Use our sourdough hydration calculator. It handles starter math, flour mix adjustments, multi-loaf scaling, and temperature-based fermentation estimates. Enter your target weight and hydration—get exact amounts in seconds. Combine with our hydration guide for the full picture.

Frequently Asked Questions

Disclaimer: Baking results vary based on flour type, ambient temperature, starter health, and technique. Use this guide and our sourdough hydration calculator as a starting point, then adjust to your conditions.